Functional control of the extrinsic pathway is mediated by tissue factor pathway inhibitor (TFPI), which binds to and inhibits factor X. For hemostatic processes to continue, factor VIIa must be able to promote the chemical conversion of factor X into factor Xa. TFPI effectively blocks this action, thereby controlling the initiation of the common pathway.
The prothrombin time (PT) test is used to monitor the extrinsic pathway and the activity of the oral anticoagulant warfarin (also known as Coumadin®).
